This invention relates generally to printed circuit board (PCB) connectors, and more particularly to high performance PCB edge connectors, systems and methods.
The use of electronics has become ubiquitous, finding its way into all manners and shapes of devices and appliances ranging from toasters to super-computers. Most electronic circuitry is now implemented with their active and passive devices coupled together by a printed circuit board (PCB). This is true whether the electronic circuitry being implemented is primarily analog in nature, digital in nature, or a hybrid of the two.
In its simplest form, a PCB is a relatively thin sheet of a dielectric (i.e. electrically non-conductive) material such as a resin-filled fiberglass. Metal lines or xe2x80x9ctracesxe2x80x9d are typically formed on one or more surfaces of the fiberglass to provide electrical connections between the various components of the electronic circuit.
Printed circuit boards can be xe2x80x9cone sided,xe2x80x9d in which all of the traces are formed on one side of the dielectric sheet of material. PCBs can also be xe2x80x9ctwo sided,xe2x80x9d where traces are formed on both sides of the sheet of dielectric material. Furthermore, PCBs can be xe2x80x9cmulti-layerxe2x80x9d where multiple dielectric layers are sandwiched between conductive layers, which may form traces or which may form grounds and/or power planes. With multi-layer boards it is common to provide electrical connections between various layers by the formation of xe2x80x9cviasxe2x80x9d (conductive plugs between metal layers) or through-holes through which conductors can be threaded.
Commonly, an electronic circuit implemented on a PCB is connected to other devices. These may be input/output devices, other electronic circuits supported on other PCBs, transmission lines, etc. While such devices could be connected directly to the PCB (such as being soldered to some of its traces or bonding pads), most commonly the connection to external devices or circuits is through a removable connector assembly. Electrical connectors of various types have been developed through the years for just this purpose.
FIGS. 1 and 2 illustrate a connection system of the prior art. This particular connection system is known as a single connector attachment or xe2x80x9cSCAxe2x80x9d and was primarily designed to replace the older Small Computer System Interface or xe2x80x9cSCSIxe2x80x9d connector design, which was not designed for modern high-frequency digital circuit operation.
In FIG. 1, a PCB 10 including traces, 12 formed on a dielectric body 14 has a male SCA connector 16 attached to its upper surface 18. The male connector 16 includes a support 20 having a number of electrical contacts 22 and a surrounding shroud 24. The SCA male connector 16 is also provided with a pair of alignment posts 26a and 26b. 
In FIG. 2, a PCB 28 provided with traces 30 on a dielectric substrate 32 includes a female SCA connector 34. The female connector includes a slot 36 provided with a plurality of contacts 38. The slot 36 is receptive to the support 20 such that when the support 20 engages with the slot 36 the contacts 22 of the male connector 16 engage with the contacts 38 of the female connector 34. The shroud 24 of the male connector 16 surrounds the body 40 of the female connector 34. The male connector 16 is guided into and locked in place with the female connector 34 by the alignment post 26a and 26b aligning with and engaging the alignment columns 42a and 42b of the female connector 34.
The contacts 22 are in electrical contact with some of the traces 12 of the printed circuit board 10. This can be accomplished with a surface mount technology (SMT) if the traces are formed on the same side of the printed circuit board as the male connector 16, or with pin-through technology if the traces 12 are formed on the opposite side of the PCB 10 from the connector 16. In the present example, a surface mount technology is illustrated. Likewise, the electrical contacts 38 connect to certain ones of the traces 30 at printed circuit board 28. Thus, when the male connector 16 is engaged with the female connector 34, the printed circuit boards 10 and 28 are in electrical communication.
It should be noted that while the SCA connectors are shown to be attached to two different PCB boards, one of the SCA connectors, such as the male SCA connector 16, could, instead, be coupled to a cable, such as a ribbon cable. In this fashion, the SCA connector can be used to couple physically separated electronic devices.
Two-piece connectors such as the SCA connectors illustrated in FIGS. 1 and 2 have several advantages. For one, they are mechanically guided and secured which aids in the engagement and the retention of the engagement of the connector system. For another, since they are typically made from metal, they are well-shielded by, for example, the body of their connectors and by the shroud 24 of the male connector. This helps reduce electromagnetic radiation and, therefore, electromagnetic interference (EMI). However, these connectors suffer from a number of drawbacks including cost, size, and an impedance matching problems generated by the wide separation between the ground planes of the two electronic circuits being coupled together caused by the connectors.
Another connection technology of the prior art is illustrated in FIG. 3. In this figure, a first PCB or xe2x80x9cplug-in boardxe2x80x9d 44 includes a male edge connector portion 46. This edge connector 46 is simply a portion of the PCB with a number of traces 48 that serve as contacts with contacts of a female edge connector. In this particular illustrated example, the edge connector has a first portion 50 and a second portion 52 separated by a slot 54. There are also unslotted variants of edge connectors in the prior art.
The female edge connector 56 is preferably coupled to a PCB 58 having traces on its bottom surface 60 (not shown), traces can also be located on a top surface 59 of PCB 58. Pins 62 of the female edge connector 56 extend through holes 64 drilled through the printed circuit board 58 and are soldered to traces or bonding pads at the end of traces on the bottom surface 60. The female edge connector 56 is provided with a pair of slots 66 and 68 including a number of contacts 70 which couple to the pins 62.
In operation, the first portion 50 of the male edge connector 46 engages the slot 66 of the female edge connector 56, and the second portion 52 of the male edge connector 46 engages with the slot 68 of female edge connector 56. In this way, the traces 48 of plug-in board 44 are in electrical contact with the contacts 70 and, therefore, the traces (not shown) of PCB 58.
The edge connector technology illustrated in FIG. 3 has certain advantages, including the elimination of a separate male connector. This not only reduces cost, but it also brings the ground planes of the two PCBs closer together, which can be advantageous, particularly in high frequency applications. However, the ground planes are still separated by the body of the female edge connector 56, thus reducing high-frequency performance.
An ever-increasing percentage of electronic circuitry is at least partially digital in nature. Furthermore, digital circuitry is operating at ever higher frequencies. For example, at the dawn of the computer age electronic circuitry was operating in the megahertz frequency range, while now it is not uncommon for circuitry to operate in the gigahertz and above frequency range. The operation of electronic circuitry at high frequencies creates a whole host of problems including EMI, cross coupling, data integrity, losses, reflections, etc.
One way of addressing the special needs of high frequency electronic circuit operation is the use of differential pairs to carry high frequency digital data. Differential pairs are typically labeled plus (+) or minus (xe2x88x92) where the plus line is used to carry the charge comprising the signal to the intended destination, and the minus line is used to carry the return charge. If two devices are communicating back and forth with each other, there may be a transmit differential pair and a receive differential pair to handle the two-way dialog.
The advantage of the differential pair is that the flux in the return line tends to cancel the flux in the transmission line. This reduces cross-coupling and radiation losses and, therefore, EMI as well. Differential routing is therefore a very desirable technique for use with digital electronic circuitry operating at high frequencies.
Routing high-speed differential signals on a circuit board can be accomplished by two philosophies; tightly coupled differential routing, or loosely coupled differential routing. Tightly coupled routing relies on the direct flux coupling between the differential pairs by placing the traces close enough to each other to achieve the desired differential impedance. The main drawback to this approach is that the slightest variation in trace spacing will cause a dramatic change in the differential impedance. This problem is unavoidable when the distance between the differential pairs must be altered to connect to an I.C. or connector.
Loosely coupled differential trace geometry places the differential signals much closer to the ground plane then the traces are to each other. This trace geometry relies on the ground plane as the main flux coupling media, and therefore is much less susceptible to trace spacing variation to control the impedance. Thus, in general, the use of loosely coupled differential traces are preferable over tightly coupled differential traces. The problem that occurs when using loosely coupled differential trace geometry is that when a differential pair passes through a connector system the ground plane is interrupted causing a significant impedance discontinuity. The problem of maintaining the flux coupling between a loosely coupled differential pair through any connector system is the main drawback to loosely coupled trace geometry.
The problem of impedance discontinuity through a loosely coupled differential connector system can be minimized through one of two methods: 1) create an artificial ground plane within the connector body; or 2) reduce the size of the uncoupled signal length to an extremely small distance to minimize the physical size, and therefore the magnitude, of the discontinuity. The first method, the artificial ground plane, has numerous previous implementations, most of which perform poorly or are very expensive. One example of this first method is the MICTOR (matched impedance connector) product of the TYCO company of Exeter, N.H. The second method has no known prior art because of the recent development of high-speed differential interfaces, and the recent understanding of the advantages of loosely coupled differential geometry. The problem with existing technology for physically small connector interfaces is either the designs are not robust enough for a hot swap environment, or they are designed for single ended signals and therefore have poor differential impedance control.
One company to address to this problem is the Molex Company of Lysle, Ill. The Molex connector, which can be purchased under the trademark betaphase or under the product name NextStep, includes a capton or flexible strip made in two layers with a ground plane underneath and connectors on top. The betaphase connector therefore carries the ground plane through the connector, reducing impedance matching problems. However the betaphase connector is extremely expensive, and would only be considered for the most critical of applications where cost was not considered to be a factor.
What the prior art does not address is a simple, inexpensive edge connector system for connecting a plug-in board to a mother board while maintaining the ground plane of the plug-in board in very close proximity to the ground plane of the mother board. The prior art has also not provided a female edge connector which can be configured to accommodate different thicknesses of plug-in board male edge connectors.
The present invention addresses the problems inherent in prior art solutions with a variation on a card edge connector system which reduce the physical size, and therefore the magnitude, of the discontinuity. Reducing the distance of the signal path that is not directly over a ground plane is a primary goal of the present invention.
In the present invention, a female edge connector is cut into the circuit board to reduce the connector size and therefore the distance the signal path is separated from the ground plane. Preferably, the female connector is provided in two pieces. This is done, in part, so that the surface mount connector that can be attached to either side of the PCB or can even connect to both sides if one half the connector is mounted on the opposite side of the board from the other. This feature advantageously allows one controller (or other electronic circuit) to be routed on one side of the back plane, and a second controller (or other electronic circuit) can be routed on the other. For example, a disk interface can be made to connect to both sides of the back plane so it can connect to both controllers for redundancy (in this context, redundancy refers to a situation wherein if one controller fails, the disk interface is still connected to the other controller and therefore remains functional). Advantageously, the connector system of the present invention is preferably implemented with surface mount technology and with no vias or crossed traces on the printed circuit board to degrade performance.
A through-board PCB connector in accordance with the present invention includes an elongated body made from an electrically insulating material and a plurality of space contacts each made from an electrically conducting material. The elongated body has a first end, a second end, a top, a bottom, and inner side, and an outer side, and is preferably provided with a PC board alignment nub. Each of the contacts preferably includes a spring contact portion provided at the inner side of the body and a surface mount contact portion provided at the bottom of the body. The body is configured to be aligned with a connector aperture formed through a printed circuit board with the aid of the alignment nub to provide a through-board PCB edge connector.
Preferably, the body is a first body and the PCB edge connector further includes a second body made from an electrically insulating material which was also configured to be aligned with the connector aperture. Preferably, the first body is separated from the second body by a distance as appropriate, to achieve the desired space, to receive a male edge connector with plug-in board.
A printed circuit board with integral edge connector in accordance with the present invention includes a printed circuit board having a top surface and a bottom surface, an aperture formed through the printed circuit board from the top surface to the bottom surface to provide at least two edges which at least partially form a perimeter of the aperture, and a connector aligned with at least one of the edges. A PC board male edge connector can be inserted through the aperture of the printed circuit board and engage the connector to electrically couple the circuitry of a plug-in board to the circuitry of a mother board. Preferably, the aperture is rectangular and has two major edges and two minor edges, where the connector is aligned with a first one of the major edges. Also preferably, the connector is a first connector and a second connector is aligned with a second one of the major edges of the aperture. By controlling the separation between the first connector and the second connector PCBs of different thicknesses can be accommodated.
When the top surface of the PC board is provided with a first plurality of differential traces, and the bottom surface is provided with a second plurality of differential traces, the top surface can support the functionality of a first electronic circuit and the bottom surface can support the functionality of a second electronic circuit in such a fashion that no vias or through-holes are required through the printed circuit board to support the functionality of the first electronic circuit and the second electronic circuit.
An electronic system in accordance with the present invention includes a plug-in board having a male edge connector, a mother board having a top surface and an opposing bottom surface, and provided with an aperture formed therethrough to provide at least two edges which at least partially form a perimeter for the aperture. A female connector is aligned with at least one of the edges, whereby the male edge connector of the plug-in board can be inserted through the aperture of the mother board and engage the female connector. Preferably, the mother board is provided with a pair of alignment holes extending at least partially through the mother board and the female connector is provided with a pair of alignment pins adapted to engage the alignment holes to align the female connector with the aperture.
A method for making a printed circuit board with integral edge connector includes forming an aperture through a printed circuit board from a top surface to a bottom surface and aligning a female edge connector with the aperture whereby a PCB male edge connector can be inserted through the aperture of the printed circuit board to engage with the female edge connector. Preferably, the method also includes forming a pair of alignment holes through the printed circuit board near to the aperture to aid in the alignment of the female edge connector with the aperture.
Even more preferably, the female edge connector comes in two parts, i.e., a first female edge connector and a second female edge connector such that two opposing side of the plug-in boards male edge connector can be contacted simultaneously when it is inserted into the aperture. The first and second female edge connectors can be both electrically coupled to the same side of the mother board, or to opposite sides of the mother board.
A method for connecting a plug-in board with a mother board in accordance with the present invention includes providing a mother board with an aperture and a female edge connector aligned with the aperture, providing a plug-in board with a male edge connector configured to extend through the aperture, and inserting the male edge connector through the aperture such that it engages the female edge connector.
As will be apparent from the preceding descriptions, the through-board PCB edge connector, system, and method provide a number of distinct advantages over the prior art. For one, the ground planes of the plug-in board and the mother board can be separated by a very small distance, e.g. a few thousandths of an inch, which improves high-frequency performance of the system in a dramatic fashion. Furthermore, the connector system is relatively inexpensive in comparison to connection systems of the prior art. So further, the current connection system is much more flexible in design than the prior art, and can be used to accommodate plug-in boards of various sizes, configurations, and thicknesses.
These and other advantages of the present invention will become apparent to those skilled in the art upon a reading of the following detailed descriptions and a study of the various figures of the drawing.